In a hybrid automatic repeat request method, a code sent by a sender is capable of not only error-detecting but also error-correcting to a certain extent. After a code word is received by an encoder at a receiver, its errors are detected first. If the errors are within the error-correcting capability of the code, then they are corrected automatically; if the errors are so many as to exceed the error-correcting capability of the code but they still can be detected, then the receiver sends a decision signal to the sender via a feedback channel to require the sender to retransmit information. In an orthogonal frequency division multiplex (OFDM) system, the correctness or incorrectness of transmission is indicated by an acknowledged (ACK) or non-acknowledged (NACK) control signaling in order to determine whether retransmission is required.
At present, it is specified in a long term evolution (LTE) that an ACK/NACK message associated with downlink data is transmitted in a physical uplink control channel. In a frequency division duplex (FDD) system, the proportion of uplink time slots equals to that of downlink times slots. In order to save signaling overhead, it is specified that an index of the physical uplink control channel corresponding to the ACK/NACK message is implicitly represented by a minimum index of a control channel element (CCE) where control signaling associated with downlink data is located.
A time division duplex (TDD) mode frame construct of the LTE system is provided, as shown in FIG. 1 (for convenience of description, this frame construct is referred to as frame construct hereinafter). In such frame construct, a wireless frame with a length of 10 ms is divided into two half-frames, and each half-frame is divided into 10 time slots (the indices of which are from 0 to 9) with a length of 0.5 ms, two time slots constituting one sub-frame with a length of 1 ms, and one half-frame containing 5 sub-frames (the indices of which are from 0 to 4). For short cyclic prefixes (CP) with a length of 5.21 us and 4.69 us, one time slot contains 7 symbols with a length of 66.7 us, where the length of the CP of the first symbol is 5.21 us and the length of the CP of the 6 remaining symbols is 4.69 us; for a long CP with a length of 16.67 us, one time slot contains 6 uplink/downlink symbols. In addition, configuration features of the sub-frames in such frame construct will be described below.
The sub-frame 0 is constantly used for downlink transmission.
The sub-frame 1 is a special sub-frame containing 3 special time slots, which are a downlink pilot time slot (DwPTS), a guard period (GP) and an uplink pilot time slot (UpPTS), respectively, in which:                the DwPTS is used for downlink transmission and at least one orthogonal frequency division multiplex (OFDM) symbol is used for transmitting a primary-synchronization channel (P-SCH) signal;        the GP is protection time and is not used for transmit any data; and        the UpPTS is used for uplink transmission (as shown in FIG. 1).        
There exists at least the following problem in prior art.
In the TDD system, since there are many configurations for the proportional relationship between the uplink time slot and downlink time slot, the case where the uplink time slots are unequal to the downlink time slots will occur. Thus, the index of the physical uplink control channel corresponding to the ACK/NACK message can not be represented implicitly by the minimum index of the CCE. Furthermore, the message can not be sent on an appropriate physical uplink control channel.